Police said they had made more than 20 arrests at a demonstration outside the U.S. embassy in London Friday.
Twenty people had been held on suspicion of being members of a banned group while another two were detained for obstruction and violent disorder.
A Metropolitan Police spokesman declined to confirm a report that the protesters were members of Muslims Against Crusades (MAC), a fringe Islamist group.
MAC, which was banned by Home Secretary Theresa May last month, was best known for a 2010 protest during which it burned poppies on Remembrance Day and chanted British soldiers, burn in hell.
It had previously held a demonstration outside the U.S. embassy on the 10th anniversary of the 9/11 attacks on America.
The police spokesman said a small number of protesters were still outside the embassy in Grosvenor Square, central London.
(Reporting by Stephen Addison)